The presence of water in the outer dead layers of the epidermis is essential to prevent what is generally referred to as "dry skin". If water is depleted from the stratum corneum more rapidly than it is received from the lower layers of the epidermis, the skin becomes dehydrated and loses its flexibility. Moisturizing compositions are essential and quite effective in restoring water lost from the stratum corneum and thereby prevent the above conditions.
One of the more important properties of a moisturizer composition is its substantivity or staying power, that is, the ability to form a film or coating which will remain on the skin even after washing. The actives which may be present, such as protein, urea and/or glucose and/or other reducing sugars, bind with water and aid in forming the film or coating. However, many moisturizer compositions available today are non-greasy compositions which are difficult to detect once applied to the skin. Thus, the user of such compositions may not be aware that the moisturizing film or coating has been washed off or otherwise removed and as a result may develop dry skin. To avoid this problem many users of such moisturizer composition may randomly apply same to the skin several times throughout the day regardless of the substantivity of the moisturizing composition.
Until now, there was no known accurate, simple, quick technique available for determining the presence of moisturizer on the skin and when additional moisturizer is necessary to avoid dry skin and therefore should be applied.